Lithogaphic printing plate



p 1963 R. N. WOODWARD 3,402,045

LITHOGRAPHI C PR INTING PLATE Filed July 27, 1964 I4 I4 11 g EMULSION 1or-SUPPORT F G I 14 I4 J I! EMULSION l0 SUPPORT UNTANNED COLLOID IOWASHED OFF SUPPORT ROBERT N WOODWARD INVENTOR.

BY fim/m AT TORNEY$ United States Patent 3,402,045 LITHOGRAPHIC PRINTINGPLATE Robert N. Woodward, Rochester, N.Y., assignor to Eastman KodakCompany, Rochester, J. .Y., a corporation of New Jersey Filed July 27,1964, Ser. No. 385,364 19 Claims. (CI. 9633) ABSTRACT OF THE DISCLOSUREA lithographic printing plate comprises a support having a hydrophobicsurface which may be a polymeric material such as polyethylene,polypropylene, cellulose acetate, polyester, etc., and having thereon anunhardened light sensitive silver halide emulsion containing a watersoluble substituted hydroquinone silver halide developing agent such asbromohydroquinone, chlorohydroquinone, toluhydroquinone,morpholinemethyl hydroquinone, etc., which forms hydrophilic areas upondevelopment.

This invention is concerned with lithographic plates, more articularlylithographic plates utilizing a hydrophobic surface having thereonhyd'rophilic image areas.

Various methods of making lithographic plates are known in which thesupport has a hydrophilic surface, wherein the image areas arehydrophobic. For instance, in the colloid transfer system, a softgelatin image is transferred from a moist developed silver halideemulsion to a hydrophilic support. In other systems, light sensitivecompounds such as diazo resins are employed which become hardened onexposure to light, so that the unexposed areas can be removed bywashing. In these systems the support is hydrophilic whereas the imageis either hydrophobic or is rendered hydrophobic by lacquering or someother treatment.

It has also been desirable to have a projection speed emulsion for usein the preparation of lithographic plates which could be used forprinting a positive image. The customary direct positive emulsionsemploying the Herschel effect to obtain a positive image from directexposure are relatively slow, so that when higher speed is required, anegative is often made and the positive printing plate prepared fromthis negative.

An alternative method of preparing a plate for making a positiveimpression has been to employ a more complex photographic element asdescribed in US. application Ser. No. 861,125, filed Dec. 21, 1959.

It has been desirable to prepare a plate which could employ a relativelyhigh speed emulsion and which would result in a simple high speed directpositive printing plate.

I have found a method of using a silver halide emulsion on a hydrophobicsupport to provide a lithographic plate having a hydrophilic imagethereon, which can be used for making right reading positiveimpressions.

One object of this invention is to provide a lithographic reproductionsystem utilizing plates with hydrophobic surfaces. An additional objectis to provide a plate capable of producing right reading negative imagesinstead of the normal positive right reading images. A further object isto provide a silver halide emulsion which, when developed, produces ahydrophilic image with respect to a hydrophobic base. A still furtherobject is to provide a method of making a lithographic plate having ahydrophobic base and hydrophilic image areas. Additional objects will beapparent from the following disclosure.

The above objects are attained by employing a hydrophobic support whichis receptive to greasy printing inks. Suitable organic polymericmaterial may be coated on a base such as paper, and the like. Of course,the support can be composed solely of the polymeric material, or a3,402,045 Patented Sept. 17, 1968 suitable laminate, as long as thesurface is oleophilic. The support may be pigmented or may betransparent to provide for exposure through the support.

The hydrophobic surface is treated to obtain adhesion to a silver halideemulsion by methods known for improving the adhesion of hyydrophobicmaterials such as electron bombardment, flame treating, oxidation withsulfuric acid-dichromate solution, treatment with chlorine gas, hydrogenperoxide, nitric acid, etc.

Over the polymeric hydrophobic surface is coated a silver halideemulsion. The light sensitive silver halide emulsion is preferablysilver chloride or silver chlorobromide but may be any of those known inthe art, such as silver bromide, silver iodide, silver bromoiodide andsilver chlorobromoiodide. The emulsion may contain the water solublesubstituted hydroquinone tanning developing agent in an amount of 2050g./Ag mole which resuits in forming a hydrophilic image upondevelopment, such as bromohydroquinone, chlorohydroquinone,toluhydroquinone, morpholinomethyl, hydroquinone, etc. however, if theemulsion does not contain the developing agent, it may be developed in abath containing as the developing agent, a water soluble substitutedhydroquinone such as bromohydroquinone, chlorohydroquinone,toluhydroquinone, morpholinomethyl hydroquinone, etc.

To increase sharpness it may be desirable to include an antihalationpigment or dye in the emulsion. Typical dyes and pigments used inantihalation layers may be used provided they are inert to the emulsionand do not affect the tannning of the emulsion. In a preferredembodiment, a carbon pigment is used. A useful amount of antihalationdye or pigment is 20-50 g./ silver mole.

It will be understood that the emulsion can be sensitized chemically,spectrally, etc., as is well known. It can be coated using methods knownin the art, but must be substantially unhardened so that the unexposedand untanned areas can be washed off after development with the tanningtype silver halide emulsion.

Although gelatin is the preferred embodiment for the colloid in whichthe silver halide is dispersed, it will be appreciated that othercolloid materials may be used providing the silver halide carryingcolloid is alkali permeable and can be hardened with a silver halidehardening type developer. The coverage of the silver halide emulsion isnot critical and can be varied depending upon the use intended. A usefulrange is about to 800 milligrams per square foot of gelatin preferably100 to 400 and about 50 to 200 milligrams per square foot of silver assilver halide, preferably 50 to 125.

Unhardened direct positive emulsions of the type described by P. J.Hillson in US. Patent 3,062,651 may be utilized to obtain directpositive images.

If the developing agent is incorporated in the silver halide emulsion orin a contiguous layer, the development is attained by using an alkalinedeveloper.

Typical activator baths for the photographic emulsion containing thedeveloping agent comprise, for example, an equeous solution of analkaline solution, such as, sodium carbonate, sodium hydroxide,potassium carbonate, potassium hydroxide, etc. Suitable baths cancomprise, for example, an aqueous solution containing about 1% sodiumhydroxide.

Typical of the activator solutions which can be used in my process arethose disclosed in U.S. Patents 2,596,754, 2,596,756, 2,725,298,2,739,890, 2,763,553, 2,835,575, 2,852,371 and 2,865,745.

It will be appreciated that any of the known hydroquinone compoundswhich have alkali splittable groups thereon to stabilize thehydroquinone during storage, but which cleave to form a water solublesubstituted hydroquinone such as bromohydroquinone, chlorohydroquinone,toluhydroquinone, morpholinomethyl hydroquinone, etc. may beincorporated in the emulsion. These compounds may be used in whole or inpart to replace the water soluble substituted hydroquinone incorporatedin the silver halide emulsion or in a contiguous layer.

It will also be appreciated than an auxiliary developing agent can beused in an amount of -20% of the substituted hydroquinone along with thesubstituted hydroquinone developing agent in order to improve the speedwithout affecting the operation of my invention.

Typical auxiliary agents include 3-pyrazolidone developing agents knownin the art as well as Elon (N-methylp-aminophenol sulfate), and thelike. Useful axuiliary agents are lphenyl-3-pyrazolidone and1-phenyl-4,4-dimethyl-3- pyrazolidone.

Suitable hydrophobic surfaces comprise such materials as polyethylene,polystryrene, cellulose esters, such as cellulose acetate, polyesters,polytetrafluoroethylene, polystyrene-butadiene, etc.

Photographic developing out silver halide emulsions in this inventioncan also contain such addenda as chemical sensitizers, speed increasingcompounds, reducing agents, sensitizing dyes, etc., which are known tothose skilled in the art. They may be blue sensitive, orthochromatic,panchromatic, infrared sensitive, etc.

By substantially unhardened colloi is meant colloid which is not harderthan would be the case of gelatin containing 0.25 ounce of formaldehyde(40% diluted 1:3 with water); or 0.7 gram dry formaldehyde per poundwhen freshly coated; or 0.1 ounce of the solution per pound for a sampleaged three to six months. It will also be appreciated that the resistantimage can be treated with hardeners or other known materials in order tomake the image more resistant to abrasion or the like when used forprinting.

The drawing shows a preferred embodiment of my invention.

FIG. 1 discloses a support having thereon an exposed silver halidephotographic emulsion 11 showing a latent image 14.

FIG. 2 shows the same photographic element of FIG. 1 after thedevelopment with a tanning silver halide developer which renders theexposed areas water insoluble and hydrophilic.

FIG. 3 shows the image areas 14 in tanned colloid remaining after theuntanned colloid in the non-image areas has been washed off.

The following examples are intended to illustrate my invention but notto limit it in any way.

Example 1 A support is prepared having a formaldehyde free paper basecoated with clear polyethylene on one side and colored or pigmentedpolyethylene on the other. The colored polyethylene contains a coloringagent such as titanium dioxide, baryta, carbon black, red dye, etc. Thesurface of the colored polyethylene is electron bombarded to obtainadhesion to a silver halide emulsion. Over the colored polyethylenelayer is coated a projection speed silver chlorobromidegelatino-emulsion containing bromohydroquinone having a silver coverageof 80 milligrams per square'foot, gelatin coverage of 139 milligrams persquare foot and a bromohydroquinone coverage of milligrams per squarefoot.

The silver halide emulsion is exposed in the prismtype process cameraand activated in an alkaline activator whereby the gelatin is tanned bythe oxidation products of the bromohydroquinone to produce areas oftanned and untanned gelatin resulting in a right reading negative of theoriginal. The unexposed soft gelatin is removed with warm water at atemperature of 90 F. The lithographic plate is then put on alithographic press using 1% phosphoric acid fountain solution, inkedwith a greasy printing ink and printed with the water adhering to theimage and the ink adhering to the hydrophobic base in the nonimageareas.

Example 2 Polystyrene, polypropylene, polyesters, styrenebutadienecopolymers and cellulose acetate are substituted for polyethylene withsimilar results as in Example 1.

EXAMPLE 3 A product according to Example 1 is made in which additives tothe gelatin are incorporated to make the gelatin image more receptive.For example, compounds which are used are silica, sugars, and salts ofheavy metals (e.g., lead acetate and zinc nitrate). These are used inamounts up to 20 milligrams per square foot in the silver halideemulsion.

EXAMPLE 4 A structure is prepared according to Example 1 except that acarbon dispersion is incorporated in the silver halide emulsion and theemulsion coated over a clear cellulose triacetate support. The carbonacts as an antihalation agent during the exposure step. Instead ofwashing the soft untanned gelatin from the developed emulsion, thesilver halide emulsion is contacted while still moist against a paperreceiving sheet so that the untanned areas adhere to the receivingsheets leaving the image areas adhering to the cellulose triacetatesurface. The resulting product provides a hydrophobic support which isoleophilic having thereon hydrophilic image areas.

EXAMPLE 5 A plate according to Example 1 is prepared except thatunsubstituted hydroquinone itself is used, it is found to beunsatisfactory due to its poor ability to render the image hydrophilicwith respect to the base. Moreover, unsubstiuted hydroquinone readilyoxidizes, particularly when used alone. When unsubstituted hydroquinoneis incorporated in a silver halide emulsion, it has a tendency tosublime and to leach out before development occurs. For these reasons,unsubstituted hydroquinone cannot be used in carrying out the invention.

EXAMPLE 6 A paper support was prepared having a water resistant coatingas described in Murphy and Wood U.S. Patent 3,021,214, issued Feb. 13,1962. Over the latex coating was coated a projection speed silverchlorobromide gelaino emulsion containing bromohydroquinone havingsilver coverage of mg. per square foot, gelatin coverage of 1.39 mg. persquare foot and a bromohydroquinone coverage of 20 mg. per square foot.

When the silver halide emulsion was exposed and processed as in Example1, the image areas were found to be 'hydrophilic with respect to greasyprinting ink, whereas the greasy printing ink adhered to the latexcoating in the non-image areas. When used on a lithographic press,right-reading positive prints were obtained.

Murphy and Wood U.S. Patent 3,021,214 is incorporated herein byreference. The coatings described therein are particularly useful informing a support which is receptive to greasy printing inks when usedwith a hardening developer which forms hydrophilic image areas.

For some purposes it may be desirable to have a negative image printedwith respect to the image to which the sensitized lithographic plate isexposed. A suitable element may be prepared having a first layer on thehydrophobic surface comprising a fogged silver halide light sensitiveemulsion. Over this fogged emulsion is coated a light sensitive silverhalide emulsion. Both emulsions must be substantially unhardened andmust be developed using a water soluble substituted hydroquinone silverhalide developing agent of this invention. A particularly usefulembodiment has the water soluble substituted hydroquinone developerincorporated in the top emulsion layer so that the exposed element canbe developed by immersing in an alkaline activator. The exposed areas inthe top emulsion layer became developed and hardened permitting theunused developer to develop and harden the fogged emulsion layerimagewise in those areas directly underneath the unexposed areas of thetop emulsion layer. Upon washing in warm water, the top layer, as wellas the unhardened areas of the fogged emulsion layer, are removed toprovide a lithographic plate having hydrophilic image areas and anoleophilic surface. When this lithographic plate is used for printing ona lithographic printing press, the printed impressions will be negativewith respect to the image to which the element was exposed initially.

The inks, which are useful in making lithographic prints on alithographic press with the plates of this invention, are not criticalprovided they are greasy inks. Typical inks which are operative includeVan Son ink, Multigraph ink ML 36, A. B. Dick 21010 ink, etc.

Fountain solutions known in the art may also be used. For instance,fountain solutions disclosed in Van Dusen US. Patent 2,393,875, issuedJan. 29, 1946, are useful solutions.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention .as described hereinabove and as defined in the appendedclaims.

I claim:

1. A photographic element comprising a support having a hydrophobicsurface having thereon an unhardened light sensitive silver halideemulsion and integral therewith a water soluble substituted hydroquinonesilver ha lide developing agent which forms hydrophilic areas upondevelopment selected from the class consisting of bromohydroquinone,chlorohydroquinone, and morpholinomethyl hydroquinone.

2. An element of claim 1 in which said emulsion is a direct positiveemulsion.

3. An element of claim 1 in which the developing agent isbromohydroquinone.

4. An element of claim 1 in which the developing agent ischlorohydroquinone.

5. An element of claim 1 in which the developing agent ismorpholinomethyl hydroquinone.

6. An element comprising a ployethylene surface having thereon anunhardened light sensitive silver halide emulsion and integral therewitha water soluble substituted hydroquinone silver halide tanningdeveloping agent selected from the class consisting ofbromohydroquinone., chlorohydroquinone, and morpholinomethylhydroquinone.

7. An element comprising a polyethylene surface having thereon anunhardened light sensitive silver halide emulsion containingbromohydroquinone.

8. An element comprising a polyethylene surface having thereon anunhardened light sensitive silver halide emulsion containingchlorohydroquinone.

9. An element comprising a cellulose triacetate surface having thereonan unhardened light sensitive silver halide emulsion and integraltherewith a water soluble substituted hydroquinone silver halide tanningdeveloping agent selected from the class consisting ofbromohydroquinone, chlorohydroquinone, and morpholinomethylhydroquinone.

10. An element comprising a polyester surface having thereon anunhardened light sensitive silver halide emulsion and integral therewitha water soluble substituted hydroquinone silver halide tanningdeveloping agent selected from the class consisting ofbromohydroquinone, chlorohydroquinone, and morpholinomethylhydroquinone.

11. An element comprising a support having thereon a coating containingsty-rene-butadiene copolymer, polystyrene and casein, and having thereonan unhardened light sensitive silver halide emulsion having integraltherewith a water soluble substituted hydroquinone silver halide tanningdeveloping agent selected from the class consisting ofbromohydroquinone, chlorohydroquinone, and morpholinomethylhydroquinone.

12. A process of forming a lithographic printing plate having ahydrophobic surface and hydrophilic image areas, comprising activatin anexposed unhardened light sensitive silver halide emulsion on saidhydrophobic surface, said emulsion having integral therewith a watersoluble substituted hydroquinone silver halide tanning developing agentselected from the class consisting of bromohydroquinone,chlorohydroquinone, and morpholinomethyl hydroquinone to form hardenedhydrophilic areas and removing unhardened emulsion areas.

13. A process of forming a lithographic printing plate having ahydrophobic surface and hydrophilic image areas, comprising activatingan exposed unhardened light sensitive silver halide emulsion on saidhydrophobic surface, said emulsion having integral therewithbromohydroquinonc, to form hardened hydrophilic areas and removing theunhardened emulsion areas.

14. A process of forming a lithographic printing plate having ahydrophobic surface and hydrophilic image areas, comprising activatingan exposed unhardened light sensitive silver halide emulsion on saidhydrophobic surface, said emulsion having inte ral therewithchlorohydroquinone, to form hardened hydrophilic areas and removing theunhardened emulsion areas.

15. A process of forming a lithographic printing plate having ahydrophobic surface and hydrophilic image areas comprising activating anexposed unhardened light sensitive silver halide emulsion on saidhydrophobic surface, said emulsion having integral therewithmorpholinomethyl hydroquinone, to form hardened hydrophilic areas andremoving the unhardened emulsion areas.

16. A process for providing a lithographic printing plate having ahydrophobic surface and hydrophilic image areas, comprising developingthe exposed unhardened light sensitive silver halide emulsion on saidhydrophobic surface with a water soluble substituted hydroquinone silverhalide tanning developing agent selected from the class consisting ofb-romohydroquinone, chlorohydroquinone, and morpholinomethylhydroquinone to form hardened hydrophilic areas and removing theuntanned emulsion areas.

17. A process for providing a lithographic printing plate having ahydrophobic surface and hydrophilic image areas, comprising developingthe exposed unhardened light sensitive silver halide emulsion on saidhydrophobic surface With a bromohydroquinone silver halide tanningdeveloping agent to form hardened hydrophilic areas and removing theuntanned emulsion areas.

18. A process for providing a lithographic printing plate having ahydrophobic surface and hydrophilic image areas, comprising developingthe exposed unhardened light sensitive silver halide emulsion on saidhydrophobic surface with a chlorohydroquinone silver halide tanningdeveloping agent to form hardened hydrophilic areas and removing theuntanned emulsion areas.

19. A process for providing a lithographic printing plate having ahydrophobic surface and hydrophilic image areas, comprising developingthe exposed unhardened light sensitive silver halide emulsion on saidhydrophobic surface with a morpholinomethyl hydroquinone silver halidetanning developing agent to form hardened hydrophilic areas and removingthe untanned emulsion areas.

References Cited UNITED STATES PATENTS 3,053,658 9/1962 Spencer 96333,146,104 8/1964 Yackel et al. 96-33 NORMAN G. TORCHlN, PrimaryExaminer.

R. E. MARTIN, Assistant Examiner.

